Strip-based electrochemical sensors for quantitative analysis of analytes

Methods, systems, and devices are disclosed for providing test strip electrochemical sensors for rapid quantitative analysis of analytes in physiological fluids. In one aspect, an electrochemical sensor includes a substrate; an electrode contingent including a first electrode having a coating of carbon nanotubes (CNTs) and a second electrode on the substrate; and an entrapment layer formed on the first electrode to attach an enzymatic substance capable of causing a redox reaction in the presence of a target analyte of a fluid sample which produces a redox-active product, in which the entrapment layer is structured to include a conductive polymer film that is reversibly dopable to conduct charge carriers across the entrapment layer and at the first electrode. For example, the electrochemical sensor can be provided on a disposable test strip to quantify L-DOPA levels in whole blood, plasma, or serum samples.